The connections of conveyor belts are generally viewed as areas of a conveyor system which deserve particular attention with regard to their serviceability and durability. This resides in the fact that, in this area, the tensile forces of the tension member in the form, of cords made of steel or aramid or in the form of a single-layer or multilayer fabric cross over into the elastomer material in the connection and in turn into the tension member of the following belt length. Here, the belt tensile force will load both the elastomer material with shear stresses and also the adhesion between the elastomer material and the tension member. It is additionally necessary to assume that the stress distribution within the connection and in the transition regions will not be homogeneous, so that there will always be areas from which failure of the connection can originate after a correspondingly long period of use.
Since the failure of a conveyor belt connection represents a very large potential hazard and a considerable economic risk, such events must be avoided. The operators of the conveyor belt systems therefore demand monitoring devices fox conveyor belt connections which give notice of a starting failure in good time and permit maintenance measures to be introduced before breakage of the connection occurs.
Apart from regular inspections, in which external damage is detected visually, continuous, automatic monitoring of the entire connection length or individual discrete zones of the connection is recommended, which, for example in the case of multi-stage steel cord belt connections, can be the deflection zones and what are known as repeats. Here, the starting point will be the supposition that, in normal operation (not under extreme overload!), a connection will not fail abruptly as a whole, rather that failure of individual areas in a connection will be assumed. In this case, the remaining intact, areas will experience a higher loading, which leads to higher stretch and therefore to an increase in the length of the loaded connection.
The lengths of the connection or reference section, measured at defined points in the conveyor belt system, must be compared with intended values and limiting values at which, if exceeded, a warning message is given or even a stoppage of the conveyor system is carried out.
Therefore, numerous developments are associated with the conveyor belt connection monitoring, reference being made in particular below to the following patent literature: DE 195 25 326 C1; U.S. Pat. No. 5,291,991; U.S. Pat. No. 4,020,945; and, U.S. Pat. No. 5,291,131.
The previously most important conveyor belt connection monitoring for use in large-scale conveyor systems is described by the document U.S. Pat. No. 6,291,991, wherein the monitoring system in this regard comprises the following components, specifically measuring marks, a measuring mark detection system, signal conditioning for the measuring mark detection system based on time measurement, an identification system with address, address detector and reader, a time measuring element, various measuring systems for determining the belt and ambient temperature and the belt tensile force and, finally, a process computer for the purpose of evaluating all the data.
The disadvantage in this case is the large number of monitoring components, individual components being susceptible to faults and, to some extent, also being difficult and costly to procure, which demonstrates the limits of the economic viability.
In the recent past, a monitoring device for conveyor belts by means of high-energy rays has therefore been advanced, which is described in particular in the following patent literature: DE 35 17 314 A1; U.S. Pat. No. 8,149,989; JP 04158208 A (Patent Abstracts of Japan); and, JP 2000292371 A (Patent Abstracts of Japan).
However, this development is still in its early stages, in particular with regard to conveyor belt connection monitoring.